In one type of thermal printing which prints colored images, a carrier contains a repeating series of spaced frames of different colored heat transferrable dyes. In such apparatus, the carrier is disposed between the receiver and a print head formed of, for example, a plurality of individual heating elements. When a particular heating element is actuated, it produces heat and causes dye from the carrier to transfer to the receiver. The density or darkness of printed colored dye is a function of the energy delivered from the heating element to the carrier.
Thermal dye transfer printers offer the advantage of true "continuous tone" dye density transfer. This result is obtained by varying the energy applied from each heating element, yielding a variable dye density image pixel in the receiver.
In order to produce a colored image, the carrier includes a repeating series of spaced colored dye frames. Such frames are often yellow, magenta and cyan dye frames. The carrier is typically mounted in a cartridge which includes take-up and supply spools. Under the control of a microprocessor, the carrier and receiver are moved past the heating elements which are selectively actuated.
There is a problem with this arrangement in that there sometimes are defective dye frames in the cartridge. If a single dye frame in a series is defective, then an unsatisfactory print will be produced by the thermal printer. Another problem is that the color dye densities in the dye frames may vary from cartridge to cartridge. Since the print head is set up for a standard series of dye frames, this also can cause less than satisfactory prints to be produced.